In general, hydrogen-storage alloy system, to be used as an electrode material for secondary battery, must have a hydrogenation characteristic such as a proper plateau pressure, high hydrogen-storage capacity and hydriding rate, and long cycle-life.
Hydrogen-storage alloy systems containing transition metal elements such as V--Ti and Ti--Mn, though they can store large amounts of hydrogen, have never been used as the electrode material for secondary battery, due to their poor hydrogen absorption/desorption behaviour in the electrolyte. The said problem is basically grounded on a phenomenon that: when hydrogen is electrochemically charged on a hydrogen-storage alloy, hydrogenation of the alloy become impossible, while the alloy system can absorb/desorb large amounts of hydrogen in a gas phase, since absorption of hydrogen is protected by the oxidized or hydroxylated surface films produced by the interaction with oxygen in the air or with hydroxide ion(OH.sup.-) in the electrolyte.
On the other hand, Fetcenko et al. describes that Ni plays a catalytic role in absorption/desorption of hydrogen for hydrogen-storage alloy in electrolyte(see: M. A. Fetcenko et al., Presentation at Electrochemical Society, 10.15(1991)).
Ezaki et al, teaches that Ti and V have the highest hydrogen evolution overpotential and Ni has the lowest one, based on the results of the hydrogen evolution overpotential determination for metals such as Ti, V, Ct, Mn, Fe, Co, Ni and Cu in 1N H.sub.2 SO.sub.4 solution(see: H; Ezaki et al., Electrochimica Acta, 38(4):557-564(1993)).
Accordingly, the hydrogen-storage alloy, to absorb hydrogen in electrolyte, must comprise an element which exists as a stable metal atom in the electrolyte and provides a catalytic effect on the electrolysis of hydrogen.
In this connection, MnNi.sub.5 and V--Ti--Zr--Ni alloy systems containing Ni which is stable in electrolyte, have been used as MH anode material for secondary battery. The electrode for secondary battery, which is prepared by the substitution of elements constituting the hydrogen-storage alloys such as Vi--Ti and Ti--Nn by Ni, has not been practically applied in the art, since the hydrogen-storage behaviour of the alloy system is not consistent in a way that plateau pressure may be increased or reversible storage capacity may be decreased.
Under the circumstances, needs have been continued to exist for the development of at electrode for secondary battery which has a charging/discharging behaviour in electrolyte and has a high discharge efficiency and energy density per unit weight.